Using skeletal muscle as an endogenous power source is an attractive approach to long-term cardiac assistance. The principle advantage of this technique over current methods is that it obviates the need for extracorporeal power sources and provides a reliable, low-cost, self- sustaining source of energy without immune compromise or loss of patient autonomy. The applicants' long-range goal is to develop a safe and reliable means to harness energy from electrically stimulate skeletal muscle in order to assist the failing heart. The objective of this application is to assemble and test (in unrestrained, conscious dugs) a prototype ventricular assist system powered by linear in situ skeletal muscle contractions. The central hypotheses to be tested is that the mechanical power of conditioned skeletal muscle can be converted into hydraulic energy at levels sufficient to drive a ventricular assist devise, in particular, on the basis of preliminary studies, skeletal muscle conditioned via long-term electrical stimulation is expected to yield roughly 2.0 mW per gram of muscle without fatigue-enough to provide substantial cardiac support. The rationale behind the proposed research centers on the fact that skeletal muscles express oxidative (fatigue-resistant) phenotypes in response to chronic activation and that these muscles have been shown to perform work at rates compatible with long-term cardiac assistance. Therefore, given the limitations of current medical therapies for congestive heart failure and the difficulties associated with delivering extracorporeal power to aid the failing heart, research to develop and test a muscle-powered blood pump is warranted. To accomplish the objectives of this research, the following three specific aims are proposed: 1) Optimize the performance, durability, and biocompatibility of a muscle energy converter (MEC) designed to transform linear muscle contractions into hydraulic energy; 2) quantify MEC efficiency and steady-state power output in vivo and assess the physiologic adaptations which occur in skeletal muscle contracting under conditions of chronic circulatory support; and 3) assemble, bench-test, and implant a complete muscle-actuated ventricular assist system compatible with the steady-state power levels measured during MEC implant studies. Upon the conclusion of this research, the applicants expect to have definitively established the steady-state work capacity of electro-stimulated skeletal muscle and for the first time demonstrated the viability of harnessing energy from in situ muscle over prolonged periods. The applicants further expect that practical application of this technology will have been demonstrated via implant testing of a complete muscle-actuated ventricular assist system.